A look at R-values

The recommended values vary tremendously based on national, provincial or municipal building codes.

R values and their metric equivalent, RSI values, are a way of labelling the effectiveness of insulating materials. The higher the R value or RSI value, the more resistance the material has to the movement of heat. Insulation products sold in Canada are labelled with R and RSI values. Provincial building codes specify minimum R (or RSI) values for new construction, with different values for different applications. It is important to know what your local building code requires when planning new construction.

The right insulation system can save your client’s money, reduce the amount of energy they use and make their home more comfortable.

R-value is a measure of resistance to heat flow through a given thickness of material. In theory, the higher the R-value, the greater that resistance. That’s fine as far as it goes.

Unfortunately, R-Value has taken hold in the consumer’s mind as a universal method for comparing insulations – the higher the R-Value, the better the insulation, end of story. But all R-Values are not created equal, because they measure only one of the factors that determine how insulation will perform in the real world.

Insulation is, first and foremost, meant to stop the movement of heat. The problem with using R-Value as the sole yardstick of an insulation’s effectiveness is that heat moves in and out of your home or commercial building in four ways: by conduction (which R-Value measures), and by convection, radiation and air infiltration (none of which R-Value measures).

The R-Values of insulation materials are measured in a lab. That would work great – if the home were inside a lab! But homes are built outdoors, and that means there are other factors like wind, humidity, and temperature changes in play. These factors create pressure differences between the interior and the exterior of the building due to things like hot air rising, wind, and mechanical systems forcing air through every tiny little opening and making its way to the interior or exterior, or to unconditioned areas of the building like attics, basements and crawl spaces.

The home or commercial building may look solid, but there are thousands of tiny gaps, cracks and penetrations between building materials. For example, if you apply the air pressure of a 20 MPH wind on a 20 deg. F day to a building, the typical R-19, fiberglass insulated wall often performs no better than the wood studs (R-6) because of air infiltration, with heat being transported around (bypassing) the fiberglass batts through convection. In very low density materials like loose blown fiberglass, heat will actually radiate right through the insulation, and this, along with convection, significantly reduces fiberglass’ installed performance and your comfort.

A superior insulation system will have good R-Value (prevent heat loss via conduction), will be pneumatically or spray applied, fully filling the building cavity (prevent heat loss via convection), and will be densely packed (prevent heat loss via air infiltration and radiation). Fiberglass meets the first criteria, but not the other three. Cellulose meets all four of these critical performance criteria!

R for R … cellulose outperforms – For a given R-value, loose cellulose weighs roughly three times as much per square foot as loose fiberglass.